1. Field of the Invention
This invention relates to a device for introducing air into an engine and, more particularly, to a setting of an air intake duct of an air intake device.
2. Description of the Related Art
Heretofore, various devices have been employed to provide an engine with air through the utilization of air intake ducts. The need for longer ducts has led to their placement in a space formed between a wheel apron and a fender. An air intake opening of the air duct is also located within this space. Such an air intake device is known from, for instance, Japanese Unexamined Patent Publication No. 61-147624.
An air duct, of considerable length can be placed in such a place, by being extended below a front side frame from the engine compartment, in order to minimize the loss of engine compartment space. By co-locating the air intake opening within this space, it is possible to supply the engine with air from this space which is cooler than air in the engine compartment.
However, locating a long air duct within a space formed between the wheel apron and fender and co-locating an air intake opening in the same space may result in causing a considerable amount of noise within the passenger compartment. The interior noise is especially annoying with an ordinary engine which is not supercharged.
The results of studies made on the causes of noise in a vehicle compartment show that pulsations of intake air are released through the air intake duct. More specifically, released pulsations of intake air are transmitted to a cowl box through a space within the wheel apron and the released pulsations are then manifest as noise in the passenger compartment through air-conditioner components located within the cowl box.
With a naturally aspirated, or ordinary, engine, the vibration of the air duct is found to contain a significant amount of low frequency vibrations, so as to cause the interior noise to become even more pronounced. On the other hand, a supercharged engine, particularly one equipped with a mechanically driven supercharger, is lacking in serious noise because a considerable amount of low frequency noise components originating in the air duct are absorbed by the supercharger.
There are two types of noise problems, i.e. noise which originates in vibrations of the air duct caused by the pulsations of intake air, which are transmitted into the passenger compartment through the car body where they are manifest as noise, and noise which is created by the pulsations of intake air which are released from an air intake opening of the air duct and transmitted into the passenger compartment where they are manifest as noise. The first type can be handled through the strategic placement of rubber mounts. However, the latter type of noise is carried through the air within the space inside the wheel apron and is transmitted to the passenger compartment. Of the two, the latter type remains the main problem.